Classical Theory of Rotational Relaxation in Diatomic Gases

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Abstract
In his well‐known theory, Parker assumes that the rotational relaxation of diatomic gases may be described by a single relaxation time which is calculated for the special case of initially nonrotating molecules. In the present theory the evolution of the rotational distribution function is described by a diffusion‐equation approximation to the master equation. This equation is linearized and solved for the case of acoustic waves. The results indicate that the absorption and dispersion of acoustic waves cannot be described by a single relaxation time. However, the behavior at very low and very high frequencies can be described in terms of “apparent relaxation times” which differ by approximately 50%. The temperature dependence of the apparent relaxation times is similar to that predicted by Parker, but the magnitudes are larger by approximately a factor of 2.